Wide bandgap semiconductors, including SiC, AlN and GaN related materials, have attracted much interest lately. In order to obtain high-quality GaN or SiC layers on Si, a growth method with different steps is used to accommodate for the large lattice and thermal mismatch between GaN and Si. AlGaN layers have been successfully used over the last years as templates for the growth of GaN on Si.
The use of an AlN buffer layer between the silicon substrate and the GaN layer is known in the prior art.
U.S. Publication No. US-2004/0119063-A1 describes a device wherein a few monolayers of aluminum are deposited on the silicon substrate to protect the silicon substrate from ammonia and then forming a nucleation layer of AlN and a buffer structure including multiple superlattices of AlGaN semiconductor having different compositions and an intermediate layer of GaN or another Ga-rich nitride semiconductor. This results in an improved crystalline structure.
On the other hand, various hydrocarbons have been applied to carbonize the silicon surface, however this requires a much higher substrate temperature and results in a rough interface between SiC and the Si surface prior to the formation of AlN. Furthermore, this method is not convenient since it requires ex situ processing steps. For example, in U.S. Publication No. US-2004/0029365-A1, a Si surface is heated and contacted by a flow of ethylene, to form a SiC layer of 50 Å (5 nm), after which a 3C—SiC layer is formed by epitaxial growth, and preferably thinned (e.g. to 5 μm) to form a platform for AlN formation. The 3C—SiC layer may also be formed directly on the Si-surface. The SiC layer formed by contacting with the ethylene flow is an example of the abovementioned layers having a bad interface with the Si-surface. For this reason, this SiC layer is not suitable for direct formation of AlN.